Valve timing control apparatus for internal combustion engine

ABSTRACT

A valve timing control apparatus for an internal combustion engine, including a drive rotation member, a follower rotation member, an electric motor, and a speed reducer including an internal gear portion, an eccentric cam on an inner peripheral side of the internal gear portion, rollers disposed between the internal gear portion and the eccentric cam, and a cage rotatable relative to the internal gear portion by rotation of the eccentric cam. A motor output shaft is arranged in series relative to the eccentric cam in an axial direction thereof. A needle bearing is rollably disposed on a part of an outer peripheral surface of the follower rotation member. The eccentric cam and the motor output shaft are press-fitted onto an outer peripheral portion of the needle bearing. The needle bearing extends over both the eccentric cam and the motor output shaft.

BACKGROUND OF THE INVENTION

The present invention relates to a valve timing control apparatus for an internal combustion engine, which variably controls opening and closing timings of an engine valve, i.e., an intake valve and/or an exhaust valve.

Recently, there has been proposed a valve timing control apparatus adapted to change a relative rotational phase between a crankshaft and a camshaft by transmitting a rotational force of an electric motor to the camshaft through a speed reducer and control opening and closing timings of an engine valve.

As well known, alternating torque is generated in the camshaft of the internal combustion engine due to a spring force of a valve spring that biases the engine valve in a closing direction of the engine valve.

For instance, Japanese Patent Application Unexamined Publication No. 2010-255543 discloses a valve timing control apparatus equipped with a speed reducer. The speed reducer includes an eccentric drive plate having a cylindrical eccentric cam on an inner peripheral side, a coupling plate, a follower plate, eccentric balls disposed between the eccentric drive plate and the coupling plate, and drive balls disposed between the eccentric drive plate and the follower plate. The eccentric balls are received in ball recesses respectively formed on the eccentric drive plate and the coupling plate. The drive balls are received in ball recesses respectively formed on the eccentric drive plate and the follower plate. By adjusting a clearance between the respective balls and the corresponding ball recesses, occurrence of noise can be suppressed even when the alternating torque generated in the camshaft is transmitted to the speed reducer.

Such adjustment of the clearance must be carried out under a condition that the eccentric cam is fitted onto an outer peripheral surface of a needle bearing disposed on an outer periphery of a cam bolt. In order to facilitate the adjustment of the clearance, a cylindrical output shaft of an electric motor and a large-diameter sleeve portion of the eccentric cam are formed separately from each other. After the adjustment of the clearance, the motor output shaft and the sleeve portion of the eccentric cam are coupled to each other to form an integral part by press-fitting in an axial direction thereof.

SUMMARY OF THE INVENTION

In the valve timing control apparatus of the above-described conventional art, in order to secure the cylindrical motor output shaft to the large-diameter sleeve portion of the eccentric cam, the motor output shaft and the large-diameter sleeve portion of the eccentric cam are integrally coupled to each other by press-fitting an inner peripheral surface of the motor output shaft onto an outer peripheral surface of the large-diameter sleeve portion. Therefore, it is necessary to increase an axial length of the motor output shaft and thereby ensure a sufficient press-fit tolerance. In such a case, when the motor output shaft is press-fitted onto the large-diameter sleeve portion, plastic deformation tends to be caused in the large-diameter sleeve portion (i.e., the eccentric cam). As a result, precision of the clearance between the respective balls and the ball recesses is deteriorated, thereby causing an unstable control condition of the valve timing control apparatus.

It is an object of the present invention to provide a valve timing control apparatus for an internal combustion engine in which the motor output shaft and the eccentric cam are integrally coupled to each other through a bearing and occurrence of plastic deformation in the eccentric cam is suppressed.

In one aspect of the present invention, there is provided a valve timing control apparatus for an internal combustion engine, the internal combustion engine including a crankshaft and a camshaft, the valve timing control apparatus including:

a drive rotation member to which a rotational force is transmitted from the crankshaft;

a follower rotation member fixed to the camshaft;

an electric motor including a rotor that is rotatable relative to the drive rotation member;

a speed reducer including a trochoid curve-shaped internal gear portion that is rotatable with the drive rotation member, a sleeve-shaped eccentric cam disposed on an inner peripheral side of the internal gear portion, the eccentric cam having an outer peripheral portion eccentric relative to a central axis thereof, a plurality of rollers disposed between the internal gear portion and the eccentric cam, and a comb-shaped cage that is rotatable with the follower rotation member, the cage supporting the plurality of rollers, the cage being rotated relative to the internal gear portion by rotation of the eccentric cam,

a tubular motor output shaft fixed to an inner periphery of the rotor, the motor output shaft being arranged in series relative to the eccentric cam in an axial direction thereof, and

a needle bearing that is rollable on a part of an outer peripheral surface of the follower rotation member,

wherein the eccentric cam and the motor output shaft are press-fitted onto an outer peripheral portion of the needle bearing, the needle bearing extending over both the eccentric cam and the motor output shaft in an axial direction thereof.

In a further aspect of the present invention, there is provided a valve timing control apparatus for an internal combustion engine, the internal combustion engine including a crankshaft and a camshaft, the valve timing control apparatus including:

a drive rotation member to which a rotational force is transmitted from the crankshaft;

a follower rotation member fixed to the camshaft;

an electric motor including a rotor that is rotatable relative to the drive rotation member;

a speed reducer including a trochoid curve-shaped internal gear portion that is rotatable with the drive rotation member, a ball bearing disposed on an inner peripheral side of the internal gear portion, the ball bearing including an outer race, an inner race having an outer peripheral surface eccentric relative to an inner peripheral surface thereof, a plurality of rollers disposed between the internal gear portion and the outer race of the ball bearing, and a comb-shaped cage that is rotatable with the follower rotation member, the cage supporting the plurality of rollers, the cage being rotated relative to the internal gear portion by rotation of the inner race of the ball bearing,

a tubular motor output shaft fixed to an inner periphery of the rotor, the motor output shaft having an axial end that abuts against the inner race of the ball bearing to thereby restrain an axial movement of the inner race of the ball bearing, and

a needle bearing that is rollable on a part of an outer peripheral surface of the follower rotation member,

wherein the inner race of the ball bearing and the motor output shaft are press-fitted onto an outer peripheral portion of the needle bearing, the needle bearing extending over both the inner race of the ball bearing and the motor output shaft in an axial direction thereof.

In a still further aspect of the present invention, there is provided a valve timing control apparatus for an internal combustion engine, the internal combustion engine including a crankshaft and a camshaft, the valve timing control apparatus including:

a drive rotation member to which a rotational force is transmitted from the crankshaft;

a follower rotation member fixed to the camshaft;

an electric motor including a rotor that is rotatable relative to the drive rotation member;

a speed reducer including at least one engagement portion, the one engagement portion being disposed in a transmission path through which a rotational force is transmitted from the electric motor, the speed reducer serving to reduce a rotational force transmitted from the rotor to an input portion and transmit the rotational force reduced to the follower rotation member,

a tubular motor output shaft fixed to the rotor;

a sleeve disposed such that an axial end portion thereof is opposed to an axial end portion of the motor output shaft, the sleeve being fixed to the input portion of the speed reducer, and

a bearing that is rollable on a part of an outer peripheral surface of the follower rotation member,

wherein the sleeve and the motor output shaft are press-fitted onto an outer peripheral portion of the bearing, the hearing extending over both the sleeve and the motor output shaft in an axial direction thereof.

According to the present invention, there is provided a valve timing control apparatus in which a motor output shaft and an eccentric cam are coupled to each other to form an integral part and occurrence of plastic deformation in the eccentric cam can be suppressed.

Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged cross-section of an essential part of a valve timing control apparatus according to a first embodiment of the present invention.

FIG. 2 is a vertical cross-section of the valve timing control apparatus according to the first embodiment of the present invention.

FIG. 3 is an exploded perspective view of the valve timing control apparatus of the first embodiment, showing main components of the valve timing control apparatus.

FIG. 4 is a cross-section of the valve timing control apparatus of the first embodiment, taken along line A-A as shown in FIG. 2.

FIG. 5 is a cross-section of the valve timing control apparatus of the first embodiment, taken along line B-B as shown in FIG. 2.

FIG. 6 is a cross-section of the valve timing control apparatus of the first embodiment, taken along line C-C as shown in FIG. 2.

FIG. 7 is a vertical cross-section of a valve timing control apparatus according to a second embodiment of the present invention.

FIG. 8 is an enlarged cross-section of an essential part of the valve timing control apparatus according to the second embodiment of the present invention.

FIG. 9 is an enlarged cross-section of an essential part of a valve timing control apparatus according to a third embodiment of the present invention.

FIG. 10 is an enlarged cross-section of an essential part of a valve timing control apparatus according to a fourth embodiment of the present invention.

FIG. 11 is a vertical cross-section of a valve timing control apparatus according to a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the accompanying drawings, first to fifth embodiments of a valve timing control apparatus for an internal combustion engine according to the present invention are explained. In the respective embodiments, the valve timing control apparatus is applied to a valve operating device for an intake valve, but the valve timing control apparatus can also be applied to a valve operating device for an exhaust valve.

As shown in FIG. 2 and FIG. 3, valve timing control apparatus 100 according to the first embodiment includes timing sprocket 1 serving as a drive rotation member that is rotated by a crankshaft of an internal combustion engine, camshaft 2 rotatably supported on a cylinder head of the internal combustion engine through a bearing (not shown) and being rotated by a rotational force transmitted from timing sprocket 1, cover 3 fixed to chain cover 64 disposed on a front end of timing sprocket 1, and rotational phase adjusting mechanism 4 disposed between timing sprocket 1 and camshaft 2 and adapted to adjust the relative rotational phase between timing sprocket 1 and camshaft 2.

Timing sprocket 1 includes ring-shaped sprocket body 1 a made of an iron-based metal material and formed with a stepwise inner peripheral surface. Gear wheel 1 b is integrally formed with an outer periphery of sprocket body 1 a and receives the rotational force from the engine crankshaft through a timing chain, not shown. Annular member 19 is disposed on a front end side of sprocket body 1 a and integrally formed with sprocket body 1 a.

Large-diameter ball bearing 43 is disposed between sprocket body 1 a and follower member (i.e., follower rotation member) 9 disposed on a front end portion of camshaft 2. Timing sprocket 1 and camshaft 2 are relatively rotatably supported through large-diameter ball bearing 43.

As shown in FIG. 2 and FIG. 3, large-diameter ball bearing 43 includes outer race 43 a, inner race 43 b and balls 43 c disposed between outer race 43 a and inner race 43 b. Outer race 43 a is press-fitted into outer race fixing portion 60 of sprocket body 1 a as explained later. Inner race 43 b is press-fitted onto inner race fixing portion 63 of follower member 9 as explained later.

Sprocket body 1 a has on an inner periphery thereof outer race fixing portion 60 that is opened toward a side of camshaft 2 and formed as an annular cutout.

As shown in FIG. 2, outer race fixing portion 60 is formed into a step shape, and includes annular inner peripheral surface 60 a extending in an axial direction of camshaft 2 and first fixing step surface 60 b extending in a radial direction of camshaft 2 on a side opposite to the open side of outer race fixing portion 60. Outer race 43 a of large-diameter ball bearing 43 is press-fitted onto inner peripheral surface 60 a in an axial direction of ball bearing 43. Inner end surface (i.e., one axial end surface) 43 d of outer race 43 a abuts on first fixing step surface 60 b, thereby carrying out positioning of outer race 43 a in one axial direction of outer race 43 a.

As shown in FIG. 2 and FIG. 3, annular member 19 is integrally formed with sprocket body 1 a of timing sprocket 1, and formed into a cylindrical shape extending from a front end portion of sprocket body 1 a on an inner peripheral side thereof toward electric motor 12 of rotational phase adjusting mechanism 4. Annular member 19 has trochoid curve-shaped internal gear portion 19 a on an inner periphery thereof. Internal gear portion 19 a has a plurality of teeth arranged at equal intervals in a circumferential direction of annular member 19. Disposed on a front end side of annular member 19 is annular female thread portion 6 integrally formed with housing 5 of electric motor 12 as explained later.

Annular retaining plate 61 is disposed on a rear end portion of sprocket body 1 a which is located on a side opposite to annular member 19. Retaining plate 61 is formed from a relatively thin metal sheet, and has an outer diameter substantially the same as that of sprocket body 1 a and an inner diameter smaller than that of inner race 43 b of large-diameter ball bearing 43.

Inner peripheral portion 61 a of retaining plate 61 is opposed to outer end surface (i.e., the other axial end surface) 43 e of outer race 43 a with a given clearance therebetween so as to cover outer end surface 43 e. Stop 61 b is disposed in a predetermined position on an inner peripheral edge of inner peripheral portion 61 a, and integrally formed with inner peripheral portion 61 a. Stop 61 b projects in a radially inward direction of retaining plate 61, that is, toward a central axis of retaining plate 61.

As shown in FIG. 3 and FIG. 5, stop 61 b is formed into a generally sector-shape, and has arcuate tip end edge 61 c formed along an arcuate inner peripheral surface of stop engaging groove portion 2 b as explained later. Retaining plate 61 has six bolt insertion holes 61 d on an outer peripheral portion thereof. Bolt insertion holes 61 d are formed at equal intervals in a circumferential direction of retaining plate 61, and extend through retaining plate 61.

Further, sprocket body 1 a (i.e., annular member 19) has six bolt insertion holes lc on an outer peripheral portion thereof. Bolt insertion holes lc are formed at equal intervals in a circumferential direction of sprocket body 1 a, and extend through sprocket body 1 a. Female thread portion 6 of annular member 19 has six female threaded hole 6 a in positions corresponding to respective bolt insertion holes 1 c, 61 d. Six bolts 7 are inserted into these holes 1 c, 61 d, 6 a, thereby securing retaining plate 61, timing sprocket 1 and female thread portion 6 (i.e., housing 5) to each other.

Sprocket body 1 a and annular member 19 constitute a casing of speed reducing mechanism 8 as explained later, and the casing and housing 5 constitute a housing unit.

Sprocket body 1 a, annular member 19, retaining plate 61 and female thread portion 6 have substantially the same outer diameter.

Cover 3 is made of aluminum alloy and formed into a cup shape. Cover 3 has swelled portion 3 a on a front end portion thereof which is formed so as to cover a front end portion of housing 5. Cylindrical wall 3 b is formed on an outer peripheral side of swelled portion 3 a, and extends along an axial direction of cover 3. As shown in FIG. 2 and FIG. 3, an inner peripheral surface of cylindrical wall 3 b defines retaining hole 3 c, and serves as a guide surface for brush retainer 28 as explained later.

Further, as shown in FIG. 2, cover 3 has flange 3 d on an outer periphery thereof. Six bolt insertion holes 3 e are formed to extend through flange 3 d, each receiving bolts 62 to thereby fix cover 3 to chain cover 64.

As shown in FIG. 2, swelled portion 3 a of cover 3 has inner peripheral step surface 3 h on a rear side thereof which is opposed to an outer peripheral surface of housing 5. Large-diameter oil seal 50 is disposed between the inner peripheral step surface of swelled portion 3 a and the outer peripheral surface of housing 5. Large-diameter oil seal 50 has a generally C-shape in cross-section, and includes a synthetic rubber base and a core plate embedded in the synthetic rubber base. Large-diameter oil seal 50 has an outer step portion on an outer peripheral side thereof which is fitted to inner peripheral step surface 3 h of swelled portion 3 a of cover 3.

Housing 5 includes housing body 5 a and sealing plate 11 that seals a front end opening of housing body 5 a. Housing body 5 a is made of an iron-based metal material and formed into a closed-ended cylindrical shape by pressing. Sealing plate 11 is made of a non-magnetic synthetic resin material.

Housing body 5 a has disk-shaped partition wall 5 b on the side of a rear end thereof, and an annular fixing groove on an inner peripheral surface of a front end portion thereof. Sealing plate 11 is fitted into the fixing groove and fixed thereto.

As shown in FIG. 2, partition wall 5 b has large-diameter shaft insertion hole 5 c that extends through a substantially central portion of partition wall 5 b. Female screw portion 6 is formed on an outer peripheral portion of partition wall 5 b, and extends in an axial direction of housing body 5 a. Annular concave portion 5 d is formed on a front end surface of partition wall 5 b and located on an inside of female screw portion 6 in a radial direction of partition wall 5 b. Annular concave portion 5 d is defined by a bottom surface and taper surface 5 e tapered relative to the bottom surface such that a diameter of annular concave portion 5 d is gradually increased. Cylindrical wall 5 f is located on a radial inside of partition wall 5 b and integrally formed therewith.

Camshaft 2 has two drive cams on an outer peripheral surface thereof which are provided each cylinder and operative to open intake valves, not shown. Further, camshaft 2 has flange portion 2 a on a front end portion thereof which is integrally formed with camshaft 2.

As shown in FIG. 2, flange portion 2 a has an outer diameter slightly larger than that of fixed end portion 9 a of follower member 9. An outer periphery of front end surface 2 e of flange portion 2 a is contacted with an axial end surface (i.e., a rear end surface) of inner race 43 b of large-diameter ball bearing 43. Camshaft 2 is coupled with follower member 9 by cam bolt 10 in such a state that front end surface 2 e is in contact with follower member 9 in an axial direction of camshaft 2.

As shown in FIG. 5, flange portion 2 a has stop engaging groove portion 2 b on an outer periphery thereof. Stop engaging groove portion 2 b extends along a circumferential direction of flange portion 2 a, and is engaged with stop 61 b of retaining plate 61. Stop engaging groove portion 2 b has a generally sector shape having a predetermined length along the circumferential direction of flange portion 2 a. Stop 61 b can be moved within a region of the length of stop engaging groove portion 2 b until both side surfaces of stop 61 b abuts against opposed surfaces 2 c, 2 d of stop engaging groove portion 2 b in the circumferential direction. By coming into abutment contact with opposed surfaces 2 c, 2 d of stop engaging groove portion 2 b, stop 61 b can serve to restrain camshaft 2 from further rotating relative to timing sprocket 1 toward a maximum phase-advance side and a maximum phase-retard side.

Stop 61 b is located closer to the side of camshaft 2 in an axial direction of retaining plate 61 than a part of retaining plate 61 which is fixed to sprocket 1 a in an axially opposed relation to rear end surface 43 e of outer race 43 a. Stop 61 b is out of contact with fixed end portion 9 a of follower member 9, thereby suppressing interference between stop 61 b and fixed end portion 9 a.

Stop 61 b and stop engaging groove portion 2 b constitute a stop mechanism.

As shown in FIG. 2, cam bolt 10 includes head portion 10 a and shaft portion 10 b connected with head portion 10 a. Shaft portion 10 b has male screw portion 10 c on an outer periphery of a tip end portion thereof. Male screw portion 10 c is screwed into female threaded hole 2 f extending inwardly from the front end portion of camshaft 2 in the axial direction of camshaft 2.

Follower member 9 is integrally formed of an iron-based metal material. As shown in FIG. 2, follower member 9 includes disk-shaped fixed end portion 9 a disposed on the side of camshaft 2, cylindrical portion 9 b concentrically projecting forwardly from a front end surface of fixed end portion 9 a, and comb-shaped cylindrical cage 41 integrally formed on an outer periphery of fixed end portion 9 a. Cage 41 retains a plurality of rollers 48 as explained later. Follower member 9 has insertion hole 9 d at a central portion thereof which extends through fixed end portion 9 a and cylindrical portion 9 b in an axial direction of follower member 9.

Fixed end portion 9 a is disposed in contact with front end surface 2 e of flange portion 2 a. Fixed end portion 9 a is press-contacted with flange portion 2 a and fixed thereto in the axial direction by an axial force of cam bolt 10.

As shown in FIG. 2, cylindrical portion 9 b has needle bearing 38 on an outer periphery thereof.

As shown in FIG. 2 to FIG. 4, cage 41 has a generally annular shape having an L-shaped cross-section. Cage 41 includes a bottom wall extending from a front side of the outer periphery of fixed end portion 9 a in a radially outward direction of follower member 9, and peripheral side wall 41 a forwardly extending from an outer periphery of the bottom portion in parallel with cylindrical portion 9 b. Side wall 41 a of cage 41 extends toward partition wall 5 b of housing body 5 a, through annular clearance 44. A plurality of roller retaining holes 41 b are formed in side wall 41 a at equal intervals therebetween in a circumferential direction of side wall 41 a. Roller retaining holes 41 b each have a generally elongated rectangular shape, serving as roller retaining portions that retain a plurality of rollers 48 so as to roll therein. The number of roller retaining holes 41 b (i.e., the number of rollers 48) is less by one than that of internal gear portion 19 a of annular member 19 by one.

Disposed between the outer periphery of fixed end portion 9 a and the bottom wall of cage 41 is inner race fixing portion 63 to which inner race 43 b of large-diameter ball bearing 43 is press-fitted and fixed.

As shown in FIG. 2, inner race fixing portion 63 is formed into a stepped cutout, and opposed to outer race fixing portion 60 in a radial direction of follower member 9. Inner race fixing portion 63 includes annular outer peripheral surface 63 a extending in the axial direction of camshaft 2, and second fixing step surface 63 b extending from a front end of outer peripheral surface 63 a in the radial direction of camshaft 2. Outer peripheral surface 63 a is contacted with an inner peripheral surface of inner race 43 h. Second fixing step surface 63 b is contacted with a front end surface of inner race 43 b. Inner race 43 b is thus held in place in inner race fixing portion 63 by the contact with outer peripheral surface 63 a and second fixing step surface 63 b.

Rotational phase adjusting mechanism 4 includes electric motor 12 as an actuator which is disposed coaxially with camshaft 2 on a front side of timing sprocket 1, and speed reducer 8 that serves to reduce rotational speed of electric motor 12 and transmit the reduced rotational speed to camshaft 2.

Electric motor 12 is a brush-equipped DC motor. As shown in FIG. 2 and FIG. 3, electric motor 12 includes housing 5 as a yoke which makes a unitary rotation with timing sprocket 1, motor shaft (i.e., output shaft) 13 as an intermediate rotor which is rotatably disposed within housing 5, a pair of semi-arcuate permanent magnet pieces 14, 15 as a stator which are fixed on an inner peripheral surface of housing 5, and stationary unit 16 fixed to sealing plate 11.

As shown in FIG. 1 and FIG. 2, motor shaft 13 is formed into a stepped cylindrical shape having a uniform wall thickness, and serves as an armature. Motor shaft 13 includes large-diameter portion 13 a disposed on the side of camshaft 2, small-diameter portion 13 b disposed on an opposite side of camshaft 2, and step portion 13 c through which large-diameter portion 13 a and small-diameter portion 13 b are connected with each other. Step portion 13 c is located in a substantially middle position in an axial direction of motor shaft 13. Core rotor 17 is fixed on an outer periphery of large-diameter portion 13 a. Small-diameter ball bearing 37 and a part of needle bearing 38 are disposed on an inside of large-diameter portion 13 a.

On the other hand, ring member 20 is press-fitted to an outer periphery of small-diameter portion 13 b and fixed thereto. Commutator 21 is press-fitted to an outer peripheral surface of ring member 20 as explained later.

Ring member 20 has an outer diameter larger than that of large-diameter portion 13 a, and an axial length slightly smaller than that of small-diameter portion 13 b. Ring member 20 and commutator 21 constitute a commutator unit.

Core rotor 17 is made of a magnetic material having a plurality magnetic poles. Core rotor 17 has on an outer peripheral portion thereof a bobbin portion having slots in which coil windings 18 a, 18 b of electromagnetic coil 18 are disposed. As shown in FIG. 2, the bobbin portion includes first jaw 17 a and second jaw 17 b respectively disposed on a front side and a rear side in an axial direction of core rotor 17. First jaw 17 a and second jaw 17 b are bent to form a generally L-shape in cross-section.

First jaw 17 a and second jaw 17 b serve to carry out positioning of coil windings 18 a, 18 b of electromagnetic coil 18 on an inner peripheral side of core rotor 17 closer to motor shaft 13. First jaw 17 a on the side of commutator 21 is located slightly offset from second jaw 17 b in a radially inward direction of core rotor 17. That is, first jaw 17 a is disposed closer to large-diameter portion 13 a of motor shaft 13, and a front end portion of first jaw 17 a is overlapped with a part of commutator 21 in the radial direction of core rotor 17 such that annular space S is generated therebetween as shown in FIG. 2. In other words, a part of a rear end portion (i.e., folded portion 21 a as explained later) of commutator 21 projects into an inner peripheral space defined by an inner peripheral surface of first jaw 17 a in the axial direction of core rotor 17 so that the annular space S is formed between the inner peripheral surface of first jaw 17 a and the rear end portion of commutator 21. In contrast, an outer peripheral portion of second jaw 17 b is engaged in annular concave portion 5 d of partition wall 5 b of housing 5.

Accordingly, electromagnetic coil 18 is wound such that coil winding 18 a on the side of commutator 21 and coil winding 18 b on the side of camshaft 2 are asymmetrically disposed with respect to core rotor 17 when viewed in cross-section taken along a rotation axis of motor shaft 13.

Specifically, coil winding 18 a is arranged in a position close to motor shaft 13 through first jaw 17 a. On the other hand, coil winding 18 b is arranged close to partition wall 5 b of housing 5 in such a state that coil winding 18 b is accommodated in annular concave portion 5 d of partition wall 5 b through second jaw 17 b. With this arrangement, it is possible to reduce an axial length of the valve timing control apparatus.

Commutator 21 is made of an electrically conductive material and formed into an annular shape. Commutator 21 is constituted of a plurality of segments. The number of the segments is the same as that of the magnetic poles of core rotor 17. Terminals drawn from electromagnetic coil 18 are electrically connected to the segments, respectively. That is, folded portion 21 a is formed on the inner peripheral side of first jaw 17 a, and serves as a connection portion in which a tip end of the respective terminals of electromagnetic coil 18 drawn through annular space S is pinched therein to allow electrical connection between electromagnetic coil 18 and commutator 21.

Permanent magnet pieces 14, 15 cooperate with each other to form a cylindrical shape, and have a plurality of magnetic poles in a circumferential direction thereof. Permanent magnet pieces 14, 15 are located in a position forwardly offset from core rotor 17 in an axial direction thereof.

Specifically, as shown in FIG. 2, a center of respective permanent magnet pieces 14, 15 in the axial direction thereof is located forwardly (i.e., toward the side of stationary unit 16) offset from a center of core rotor 17 in the axial direction thereof by a predetermined distance. With the offset arrangement, front end portions 14 a, 15 a of permanent magnet pieces 14, 15 are overlapped with commutator 21, first brushes 25 a, 25 b of stationary unit 16 (see FIG. 6) in a radial direction of permanent magnet pieces 14, 15.

As shown in FIG. 2 and FIG. 6, stationary unit 16 includes disk-shaped resin plate 22 integrally formed on an inner peripheral side of sealing plate 11, a pair of resin holders 23 a, 23 b disposed on a rear surface of resin plate 22, a pair of first brushes 25 a, 25 b slidably disposed in respective resin holders 23 a, 23 b in a radial direction of resin plate 22, inner and outer annular slip rings 26 a, 26 b concentrically disposed on front end surfaces of resin holders 23 a, 23 b, and pigtail harnesses 27 a, 27 b that electrically connect first brushes 25 a, 25 b and slip rings 26 a, 26 b with each other. First brushes 25 a, 25 b are biased by coil springs 24 a, 24 b such that tip end surfaces thereof are resiliently contacted with an outer peripheral surface of commutator 21 in the radial direction of resin plate 22. Slip rings 26 a, 26 b are respectively embedded and fixed in the front end surfaces of resin holders 23 a, 23 b such that front surfaces thereof are exposed outside.

Slip rings 26 a, 26 b and second brushes 30 a, 30 b constitute a power supply mechanism. First brushes 25 a, 25 b, commutator 21, and pigtail harnesses 27 a, 27 b constitute a current-supply changeover mechanism.

As shown in FIG. 2, sealing plate 11 is fixed to a recessed step portion formed in an inner periphery of a front end portion of housing 5 by caulking. Shaft insertion hole 11 a extends through a central portion of sealing plate 11, through which one end portion of motor shaft 13 is inserted.

Brush retainer 28 serving as a power supplying brush unit is fixed to swelled portion 3 a of cover 3. Brush retainer 28 is integrally molded from a synthetic resin material.

As shown in FIG. 2 and FIG. 3, brush retainer 28 has a generally L-shape in side view. Brush retainer 28 includes generally cylindrical brush retaining portion 28 a inserted into retaining hole 3 c of cover 3, connector portion 28 b disposed on an upper end of brush retaining portion 28 a, a pair of bracket portions 28 c disposed on both sides of brush retaining portion 28 a and fixed to swelled portion 3 a of cover 3, and a pair of terminals 31, 31 substantially embedded in connector portion 28 b.

Terminals 31, 31 are formed into a crank shape vertically extending in parallel to each other. Each of terminals 31, 31 has one end portion (i.e., a lower end portion) exposed to the side of a bottom of brush retaining portion 28 a, and the other end portion (i.e., an upper end portion) 31 b projecting into female engaging groove 28 d.

Brush retaining portion 28 a extends in a substantially horizontal direction (i.e. in an axial direction thereof). Brush retaining portion 28 a includes sleeve-shaped slide portions 29 a, 29 b fixed into cylindrical through-holes that substantially horizontally extend in upper and lower positions in brush retaining portion 28 a. Slide portions 29 a, 29 b respectively retain second brushes 30 a, 30 b so as to be slidable in an axial direction of the cylindrical holes.

Each of second brushes 30 a, 30 b has a generally rectangular prism shape. Second brushes 30 a, 30 b are respectively biased toward slip rings 26 a, 26 b in an axial direction thereof by second coil springs 32 a, 32 b such that rear end surfaces of second brushes 30 a, 30 b are respectively contacted with respective slip rings 26 a, 26 b. Each of second coil springs 32 a, 32 b is installed between a front end surface of each of second brushes 30 a, 30 b and the one end portion (not shown) of each of terminals 31, 31 exposed to a bottom of each of the cylindrical through-holes.

A rear end portion of each of second brushes 30 a, 30 b and the one end portion of each of terminals 31, 31 are electrically connected with each other through a resilient pigtail harness (not shown) welded thereto. The pigtail harness has such a predetermined length that each of second brushes 30 a, 30 b can be prevented from falling off from each of slide portions 29 a, 29 b when being urged to advance to a maximum slide position by each of coil springs 32 a, 32 b.

Further, annular seal member 34 is fitted into an annular engaging groove formed on an inner periphery of cylindrical wall 3 b of cover 3. When brush retaining portion 28 a is inserted into retaining hole 3 c of cover 3, seal member 34 is elastically pressed onto an outer peripheral surface of a base portion of brush retaining portion 28 a and seals an inside of brush retaining portion 28 a.

The other end portion 31 b of each of terminals 31, 31 is exposed to engaging groove 28 d of connector portion 28 b, and electrically connected to a control unit (not shown) through a male terminal (not shown) which is to be inserted into engaging groove 28 d.

As shown in FIG. 1 and FIG. 2, motor shaft 13 is rotatably supported by small-diameter ball bearing 37 disposed on shaft portion 10 b of cam bolt 10, and needle bearing 38 disposed on the rear side of small-diameter ball bearing 37 in an axial direction of motor shaft 13. Small-diameter ball bearing 37 is disposed on an outer peripheral surface of shaft portion 10 b on the side of head portion 10 a of cam bolt 10. Needle bearing 38 is disposed on an outer peripheral surface of cylindrical portion 9 b of follower member 9.

Small-diameter ball bearing 37 is of a generally known type. Small-diameter ball bearing 37 includes inner race 37 a, outer race 37 b and a plurality of balls 37 c disposed between inner race 37 a and outer race 37 b. Inner race 37 a is fixedly disposed between front end surface 9 e of cylindrical portion 9 b of follower member 9 and seat surface 10 d located on the rear side of head portion 10 a of cam bolt 10. On the other hand, outer race 37 b is held on an inner peripheral surface of large-diameter portion 13 a of motor shaft 13 with a slight press-fit. One axial end surface (i.e., a front end surface) of outer race 37 b is held in contact with inner peripheral step surface 13 d of step portion 13 c of motor shaft 13. Cylindrical spacer 54 is disposed between the outer peripheral surface of shaft portion 10 b on the side of head portion 10 a of cam bolt 10 and an inner peripheral surface of inner race 37 a, and between the outer peripheral surface of shaft portion 10 b and a recessed inner peripheral surface of a front end portion of cylindrical portion 9 b of follower member 9.

Needle bearing 38 includes cylindrical retainer 38 a made of iron-based metal, and a plurality of needle rollers 38 b rotatably supported in retainer 38 a.

Retainer 38 a has both axial end portions bent in a radially inward direction of retainer 38 a. Tip end portion (i.e., a rear end portion) 13 e of large-diameter portion 13 a of motor shaft 13 is press-fitted onto the side of one axial end (i.e., a front end) of an outer peripheral surface of retainer 38 a. Eccentric cam 39 is press-fitted onto the side of the other axial end (i.e., a rear end) of the outer peripheral surface of retainer 38 a. Respective needle rollers 38 b roll on the outer peripheral surface of cylindrical portion 9 b of follower member 9.

Small-diameter oil seal 46 is disposed between an outer peripheral surface of large-diameter portion 13 a of motor shaft 13 and an inner peripheral surface of cylindrical wall portion 5 f of partition wall 5 b (i.e., an inner peripheral surface defining shaft insertion hole 5 c). Small-diameter oil seal 46 separates speed reducer 8 and electric motor 12 from each other, and serves to prevent lubricating oil from leaking from an inside of speed reducer 8 into electric motor 12. An inner periphery of small-diameter oil seal 46 is elastically contacted with the outer peripheral surface of large-diameter portion 13 a, thereby applying friction resistance to motor shaft 13 during rotation of motor shaft 13.

The control unit is configured to determine an operating condition of the engine on the basis of an information signal outputted from various sensors (not shown) such as a crank angle sensor, an air flow meter, an engine coolant temperature sensor, an accelerator position sensor, etc., and control the engine. The control unit is also configured to control rotation of motor shaft 13 by energizing electromagnetic coil 18 and control a rotational phase of camshaft 2 relative to timing sprocket 1 through speed reducer 8.

As shown in FIG. 1 to FIG. 3, speed reducer 8 includes eccentric cam 39 carrying out eccentric rotation, intermediate-diameter ball bearing 47 disposed on an outer periphery of eccentric cam 39, rollers 48 disposed on an outer periphery of intermediate-diameter ball bearing 47, cage 41 that retains rollers 48 so as to roll on the outer periphery of intermediate-diameter ball bearing 47 and permits radial displacement of rollers 48, and follower member 9 integrally formed with cage 41.

As shown in FIG. 1 and FIG. 2, eccentric cam 39 is formed into a cylindrical sleeve shape having a short axial length. As shown in FIG. 4, eccentric cam 39 has a thickness varying in a circumferential direction of eccentric cam 39. That is, an inner peripheral portion of eccentric cam 39 has a generally true circle shape in cross-section, and an outer peripheral portion of eccentric cam 39 has an eccentric circle shape in cross-section which has a center offset relative to a center of the generally true circle shape. Thus, the outer peripheral portion of eccentric cam 39 has a central axis offset relative to a central axis of the inner peripheral portion thereof. The central axis of the inner peripheral portion of eccentric cam 39 is determined as a central axis of eccentric cam 39. The outer peripheral portion of eccentric cam 39 defines a cam surface. In FIG. 4, reference sign X denotes a line extending perpendicular to the central axis of the inner peripheral portion of eccentric cam 39 aligned with the central axis of motor shaft 13, and reference sign Y denotes a line extending perpendicular to the central axis of the outer peripheral portion of eccentric cam 39 in parallel to line X. The central axis of the outer peripheral portion of eccentric cam 39 is slightly offset relative to the central axis of motor shaft 13 in a radial direction of motor shaft 13.

A As shown in FIG. 1, eccentric cam 39 and large-diameter portion 13 a of motor shaft 13 are formed to have inner diameters slightly smaller than an outer diameter of retainer 38 a of needle bearing 38. Eccentric cam 39 is press-fitted onto the outer peripheral surface of retainer 38 a. Eccentric cam 39 is arranged in such a state that front end portion 39 a abuts against rear end portion 13 e of large-diameter portion 13 a of motor shaft 13 in an axial direction of eccentric cam 39, and is press-fitted onto retainer 38 a so that the whole inner peripheral surface of eccentric cam 39 is contacted with the outer peripheral surface of retainer 38 a. That is, eccentric cam 39 and motor shaft 13 are press-fitted onto the outer peripheral surface of retainer 38 a of needle bearing 38 in such a state that eccentric cam 39 and motor shaft 13 are arranged in series in the axial direction thereof. Needle bearing 38 extends over both eccentric cam 39 and rear end portion 13 e of large-diameter portion 13 a of motor shaft 13 so that the outer peripheral surface of retainer 38 a is in contact with the inner peripheral surface of eccentric cam 39 and an inner peripheral surface of rear end portion 13 e of large-diameter portion 13 a.

Metal washer 55 having a small thickness is fixedly disposed between front end portion 39 a of eccentric cam 39 and a rear end surface of large-diameter portion 13 a of motor shaft 13. Washer 55 is formed to have an inner diameter slightly larger than an outer diameter of needle bearing 38, and held on the outer peripheral surface of retainer 38 a with a slight press-fit. Washer 55 is also formed to have an outer diameter slightly larger than an inner diameter of inner race 47 a of intermediate-diameter ball bearing 47.

A plurality of through-holes 58 are formed in a position in fixed end portion 9 a of follower member 9 in which fixed end portion 9 a is opposed to eccentric cam 39 in the axial direction thereof. Through-holes 58 are arranged at substantially equal intervals therebetween in a circumferential direction of follower member 9. Through-holes 58 receive a given tool for restricting an amount of press-fit when eccentric cam 39 is press-fitted onto needle bearing 38 from the side of motor shaft 13.

Intermediate-diameter ball bearing 47 is disposed in a position where intermediate-diameter ball bearing 47 as a whole is substantially overlapped with needle bearing 38 in a radial direction thereof. Intermediate-diameter ball bearing 47 includes inner race 47 a, outer race 47 b and balls 47 c disposed between inner and outer races 47 a, 47 b. Inner race 47 a is press-fitted onto the outer peripheral surface of eccentric cam 39. Inner race 47 a is sandwiched between washer 55 and snap ring 56 fitted onto an outer periphery of a rear end portion of eccentric cam 39. Thus, inner race 47 a is held in a fixed state in an axial direction thereof by washer 55 and snap ring 56.

On the other hand, outer race 47 b is held free without being restrained in an axial direction thereof. That is, one axial end surface of outer race 47 b on the side of electric motor 12 is out of contact with any other component, and the other axial end surface thereof is opposed to the bottom wall of cage 41 with a slight first clearance C therebetween as shown in FIG. 2. An outer peripheral surface of outer race 47 b is in contact with an outer peripheral surface of respective rollers 48, and is opposed to an inner peripheral surface of side wall 41 a of cage 41 with annular second clearance C1 therebetween as shown in FIG. 2. With the provision of second clearance C1, as eccentric cam 39 is rotated, intermediate-diameter ball bearing 47 as a whole can be moved in a radial direction thereof, that is, intermediate-diameter ball bearing 47 can be eccentrically moved.

As intermediate-diameter ball bearing 47 is eccentrically moved, respective rollers 48 are moved in a radial direction thereof and brought into engagement with internal gear portion 19 a of annular member 19. Respective rollers 48 are also guided by both side edges of respective roller retaining holes 41 b and swingably moved in the radial direction thereof.

Speed reducer 8 is supplied with lubricating oil through a lubricating oil supply path. As shown in FIG. 2, the lubricating oil supply path includes oil supply hole 51 extending in camshaft 2 in the axial direction of camshaft 2, and small-diameter oil hole 52 extending through follower member 9 in the axial direction of follower member 9. Oil supply hole 51 is communicated with an oil supply passage formed in a bearing of the cylinder head, through which the lubricating oil is supplied from a main oil gallery (not shown). Oil hole 52 has one end opened to oil supply hole 51 and the other end opened to the vicinity of needle bearing 38 and intermediate-diameter ball bearing 47. The lubricating oil supply also includes three large-diameter oil discharge holes (not shown) extending through follower member 9.

With the provision of the lubricating oil supply path, the lubricating oil is supplied to and stored in clearance 44 between side wall 41 a of cage 41 and partition wall 5 b of housing body 5 a, and then supplied to moveable parts such as intermediate-diameter ball bearing 47 and respective rollers 48. The lubricating oil stored in clearance 44 is prevented from leaking into housing 5 by small-diameter oil seal 46.

Further, as shown in FIG. 2, caps 53, 57 having a generally C-shaped section are press-fitted into and cover insertion holes respectively formed at the front end of motor shaft 13 in a substantially central position of swelled portion 3 a of cover 3. A fastening jig for cam bolt 10 is inserted through the insertion holes.

An operation of valve time control apparatus 100 according to this embodiment will be explained hereinafter. When the crankshaft of the engine is rotationally driven to rotate timing sprocket 1 through the timing chain, the rotation force is transmitted to housing 5 through annular member 19 and female screw portion 6, thereby causing synchronous rotation of electric motor 12. On the other hand, the rotation force of annular member 19 is transmitted to camshaft 2 through respective rollers 48, cage 41 and follower member 9 so that the cam of camshaft 2 actuates the intake valve to be opened and closed.

When the engine is operated under a predetermined operating condition after the engine is started, the control unit outputs an exciting current to electromagnetic coil 18 of electric motor 12 through terminals 31, 31, the pigtail harnesses, second brushes 30 a, 30 b and slip rings 26 a, 26 b. Motor shaft 13 is rotationally driven so that the rotation force is inputted to speed reducer 8, and then the rotation force reduced is transmitted to camshaft 2.

Specifically, when eccentric cam 39 is rotated with the rotation of motor shaft 13, respective rollers 48 roll on internal gear portion 19 a of annular member 19 so as to move from one of the teeth of internal gear portion 19 a to the adjacent one of the teeth of internal gear portion 19 a with rolling contact therewith, while being guided in roller retaining holes 41 b of cage 41 in the radial direction of cage 41 per rotation of motor shaft 13. Respective rollers 48 move in the circumferential direction of cage 41 while repeating such rolling movement. Owing to the rolling movement of rollers 48, the rotation of motor shaft 13 is reduced, and the reduced rotation is transmitted to follower member 9. A speed reduction ratio at this time can be optionally set on the basis of the number of rollers 48.

As a result, camshaft 2 is rotated relative to timing sprocket 1 in a reverse direction to that of timing sprocket 1. Thus, a rotational phase of camshaft 2 relative to timing sprocket 1 is changed to thereby control the opening timing and the closing timing of the intake valve to a phase-advance side or a phase-retard side.

Camshaft 2 is controlled to the maximum rotational position (i.e., the maximum rotational phase position) relative to timing sprocket 1 by abutment of the side surfaces of stop 61 b of retaining plate 61 against one of opposed surfaces 2 c, 2 d of stop engaging groove portion 2 b of flange portion 2 a of camshaft 2.

Specifically, when follower member 9 is rotated in the same direction as that of timing sprocket 1 in accordance with the rotation of eccentric cam 39, one side surface of stop 61 h abuts against one surface 2 c of stop engaging groove portion 2 b to thereby restrain further rotation of camshaft 2 in the same direction. Accordingly, camshaft 2 is held in the maximum phase-advance position relative to timing sprocket 1.

On the other hand, when follower member 9 is rotated in a reverse direction to that of timing sprocket 1, the other side surface of stop 61 b abuts against the other surface 2 d of stop engaging groove portion 2 b to thereby restrain further rotation of camshaft 2 in the reverse direction. Accordingly, camshaft 2 is held in the maximum phase-retard position relative to timing sprocket 1.

As a result, the opening timing and the closing timing of the intake valve is changed to the maximum phase-advance side or the maximum phase-retard side, so that fuel economy and output of the engine can be enhanced.

Further, in this embodiment, a coil of one coil winding 18 a of electromagnetic coil 18 can be wound on first jaw 17 a from the inner peripheral side sufficiently close to commutator 21. Therefore, even if the number of turns of the coil of coil winding 18 a is increased, an amount of coil winding 18 a projecting in the axial direction can be reduced. Further, the other coil winding 18 b of electromagnetic coil 18 can be accommodated in annular concave portion 5 d of partition wall 5 b. With this arrangement, even if the number of turns of a coil of coil winding 18 b is increased, an increased amount of coil winding 18 b can be received in annular concave portion 5 d. As a result, it is possible to reduce an axial length of valve timing control apparatus 100 as small as possible.

Further, in this embodiment, small-diameter oil seal 46 is arranged between the outer peripheral surface of large-diameter portion 13 a of motor shaft 13 and the inner peripheral surface of cylindrical wall portion 5 f of partition wall 5 b. Since small-diameter oil seal 46 is effectively arranged in view of axial layout, the axial length of valve timing control apparatus 100 can be reduced to thereby enhance the installability relative to the engine.

Further, in this embodiment, motor shaft 13 and eccentric cam 39 are arranged separate from each other in the axial direction, and coupled with each other through needle bearing 38 by press-fitting the inner peripheral surfaces of motor shaft 13 and eccentric cam 39 onto the outer peripheral surface of retainer 38 a of needle bearing 38 in the axial direction. With this construction, it is possible to suppress occurrence of plastic deformation in eccentric cam 39 upon press-fitting. In contrast, in the above-described conventional art, the motor shaft and the eccentric cam are directly coupled with each other to form an integral part by press-fitting in the axial direction which tends to have a risk of occurrence of plastic deformation.

That is, eccentric cam 39 is press-fitted not to motor shaft 13 but to needle bearing 38, so that an axial length of eccentric cam 39 can be reduced. Therefore, it is possible to reduce a press-fit tolerance of eccentric cam 39 relative to needle bearing 38, and therefore suppress occurrence of plastic deformation in eccentric cam 39 upon press-fitting.

With this construction, it is possible to reduce variation of the clearance generated at mutual contact or engagement portions between intermediate-diameter ball bearing 47, respective rollers 48 and internal gear portion 19 a of annular member 19. As a result, a stable operation of speed reducer 8 can be obtained.

Further, this embodiment differs from the conventional art in that large-diameter portion 13 a of motor shaft 13 is press-fitted to not both the outer periphery of eccentric cam 39 and the outer periphery of needle bearing 38, but only the outer periphery of needle bearing 38. With this construction, an outer diameter of large-diameter portion 13 a can be sufficiently reduced to thereby increase the number of turns of the coil of coil winding 18 of core rotor 17 by an amount of reduction of the outer diameter of large-diameter portion 13 a. As a result, it is possible to maintain the size of existing valve timing control apparatus 100 and enhance characteristics of electric motor 12 without increasing an entire axial length and an outer diameter of valve timing control apparatus 100

Further, in this embodiment, an outer diameter of motor shaft 13 can be reduced whereby an outer diameter of oil seal 46 disposed on the outer peripheral surface of large-diameter portion 13 a of motor shaft 13 can be reduced. As a result, it is possible to reduce slide resistance that is caused between oil seal 46 and large-diameter portion 13 a.

Further, in this embodiment, it is possible to readily manage press-fit of motor shaft 13 and eccentric cam 39 relative to needle bearing 38, and therefore, enhance the precision of the bearing and readily adjust the clearance generated at the mutual engagement portions of speed reducer 8. Further, in this embodiment, the assembling work can be simplified, and the production process can be facilitated, thereby serving for reducing the cost.

Further, in this embodiment, washer 55 is disposed between large-diameter portion 13 a of motor shaft 13 and eccentric cam 39. Washer 55 cooperates with snap ring 56 to restrain axial movement of inner race 47 a of intermediate-diameter ball bearing 47, so that the eccentric movement of eccentric cam 39 can be transmitted with high accuracy.

Further, in this embodiment, speed reducer 8 can be supplied with the lubricating oil through oil supply hole 51 and oil hole 52, so that lubrication characteristics of respective parts of speed reducer 8 can be enhanced. That is, since the lubricating oil is supplied between internal gear portion 19 a and rollers 48, needle bearing 38, and intermediate-diameter ball bearing 47, the lubrication between needle rollers 38 b and between balls 47 c can be enhanced. Therefore, speed reducer 8 can always carry out smooth change of the rotational phase. In addition, the lubricating oil can attain a buffer function, thereby more effectively suppressing occurrence of a striking noise at the mutual contact or engagement parts of speed reducer 8.

In particular, during the operation of the engine, the lubricating oil fed from the oil pump is always supplied into clearance 44 between side wall 41 a of cage 41 and partition wall 5 b of housing body 5 a through the lubricating oil supply path, so that clearance 44 is filled with the lubricating oil. Therefore, it is possible to suppress occurrence of lack of an oil film at the rolling members such as ball bearing 47 and the slide parts. As a result, an initial drive load of electric motor 12 can be sufficiently reduced, thereby serving for enhancing a response to control of the valve timing and reducing energy consumption.

Further, in this embodiment, speed reducer 8 and electric motor 12 can be integrally formed with each other through housing 5, and further integrally formed with timing sprocket 1 through sprocket body 1 a. Therefore, these parts can constitute a one-piece unit, so that valve timing control apparatus 100 can be downsized in both the axial direction and the radial direction and can serve for ready management.

Further, in this embodiment, eccentric cam 39 is supported in such a state that eccentric cam 39 is sandwiched between needle rollers 38 b of needle bearing 38 and balls 47 c of ball bearing 47. With this construction, eccentric cam 39 can be stably supported.

Further, in this embodiment, it is possible to stably fix small-diameter ball bearing 37 and enhance axial positioning accuracy of motor output shaft 13 that abuts against outer race 37 b of small-diameter ball bearing 37 in the axial direction.

Further, in this embodiment, with the provision of through-holes 58, when eccentric cam 39 is press-fitted onto needle bearing 38 from the side of motor shaft 13, a given tool for restricting an amount of press-fit of eccentric cam 39 can be introduced through through-holes 58.

Second Embodiment

Referring to FIG. 7 and FIG. 8, valve timing control apparatus 200 according to a second embodiment will be explained hereinafter. The second embodiment differs from the first embodiment in construction of large-diameter portion 13 a of motor shaft 13 and omission of washer 55. As shown in FIG. 7 and FIG. 8, in valve timing control apparatus 200, large-diameter portion 13 a of motor shaft 13 has radial thickness Q slightly larger than that of small-diameter portion 13 b, and axial length L increased by a thickness of washer 55 of the first embodiment.

An inner peripheral side of tip end surface (i.e., rear end surface) 13 f of large-diameter portion 13 a is contacted with the front end surface of eccentric cam 39 in the axial direction. On the other hand, an outer peripheral side of tip end surface 13 f is contacted with a front end surface of inner race 47 a of intermediate-diameter ball bearing 47. Accordingly, tip end surface 13 f of large-diameter portion 13 a and snap ring 56 cooperate with each other to restrict axial movement of inner race 47 a.

In the second embodiment, washer 55 can be omitted, thereby serving for reducing the number of parts and facilitating the production process and the assembling work.

Further, a relative position between motor shaft 13 and eccentric cam 39 in the axial direction can be determined in accordance with a contact portion between large-diameter portion 13 a and eccentric cam 39.

Third Embodiment

Referring to FIG. 9, valve timing control apparatus 300 according to a third embodiment will be explained hereinafter. The third embodiment differs from the first and second embodiments in construction of needle bearing 38, large-diameter portion 13 a of motor shaft 13, and eccentric cam 39. As shown in FIG. 9, in valve timing control apparatus 300, needle bearing 38 has an outer diameter larger than those of the first and second embodiments. Further, large-diameter portion 13 a of motor shaft 13 includes annular cutout portion 13 g formed in the inner peripheral surface of tip end portion 13 e. A front side of needle bearing 38 is disposed in cutout portion 13 g. Further, eccentric cam 39 has a thickness slightly smaller than that of the first embodiment.

With the construction of needle bearing 38 having the larger outer diameter, it is possible to enhance rigidity of needle bearing 38 supporting motor shaft 13 and eccentric cam 39 and thereby increase strength of coupling between motor shaft 13 and eccentric cam 39.

Other construction of the third embodiment is the same as that of the first embodiment, and therefore, the third embodiment can attain substantially the same function and effect as those of the first embodiment.

Fourth Embodiment

Referring to FIG. 10, valve timing control apparatus 400 according to a fourth embodiment will be explained hereinafter. The fourth embodiment differs from the first embodiment in construction of needle bearing 38 and large-diameter portion 13 a of motor shaft 13, and omission of washer 55. As shown in FIG. 10, in valve timing control apparatus 400, needle bearing 38 has an outer diameter larger than those of the first and second embodiments. Further, large-diameter portion 13 a of motor shaft 13 has radial thickness Q slightly larger than that of small-diameter portion 13 b, and axial length L increased by a thickness of washer 55 of the first embodiment, like in the second embodiment. In the fourth embodiment, washer 55 can be omitted, and rigidity of needle bearing 38 supporting motor shaft 13 and eccentric cam 39 can be enhanced.

Fifth Embodiment

Referring to FIG. 11, there is shown valve timing control apparatus 500 according to a fifth embodiment. The fifth embodiment differs from the first to fourth embodiments in that inner race 47 a of intermediate-diameter ball bearing 47 serves as the eccentric cam, and eccentric cam 39 used in the first to fourth embodiments is omitted.

In the fifth embodiment, inner race 47 a is formed to have a radial thickness that gradually varies in the circumferential direction, and therefore, have an outer peripheral surface serving as a cam surface of eccentric cam 39 of the first to fourth embodiments.

Further, in the fifth embodiment, inner race 47 a is press-fitted onto the outer peripheral surface of needle bearing 38. A front end surface of inner race 47 a abuts against the tip end surface (i.e., the rear end surface) of large-diameter portion 13 a of motor shaft 13 in the axial direction of inner race 47 a, so that inner race 47 a can be restrained from moving in the axial direction (i.e., in the forward direction).

With this construction, it is possible to omit eccentric cam 39 of the first embodiment and simplify the construction. As a result, the production process and the assembling work can be facilitated.

Furthermore, in the fifth embodiment, washer 55 and snap ring 56 as used in the first embodiment can be omitted to thereby facilitate the production process and the assembling work.

The present invention is not limited to the above embodiments, and may be variously modified. It is possible to use elements other than permanent magnet pieces 14, 15 of the above embodiments.

Further, various bearings, for instance, a plain bearing, a ball bearing having plural rows of balls, etc., other than needle bearing 38 can be used.

This application is based on a prior Japanese Patent Application No. 2012-30031 filed on Feb. 15, 2012. The entire contents of the Japanese Patent Application No. 2012-30031 are hereby incorporated by reference.

Although the invention has been described above by reference to certain embodiments of the invention and modifications of the embodiments, the invention is not limited to the embodiments and modifications described above. Further variations of the embodiments and modifications described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims. 

1. A valve timing control apparatus for an internal combustion engine, the internal combustion engine including a crankshaft and a camshaft, the valve timing control apparatus comprising: a drive rotation member to which a rotational force is transmitted from the crankshaft; a follower rotation member fixed to the camshaft; an electric motor comprising a rotor that is rotatable relative to the drive rotation member; a speed reducer comprising a trochoid curve-shaped internal gear portion that is rotatable with the drive rotation member, a sleeve-shaped eccentric cam disposed on an inner peripheral side of the internal gear portion, the eccentric cam having an outer peripheral portion eccentric relative to a central axis thereof, a plurality of rollers disposed between the internal gear portion and the eccentric cam, and a comb shaped cage that is rotatable with the follower rotation member, the cage supporting the plurality of rollers, the cage being rotated relative to the internal gear portion by rotation of the eccentric cam, a tubular motor output shaft fixed to an inner periphery of the rotor, the motor output shaft being arranged in series relative to the eccentric cam in an axial direction thereof, and a needle bearing that is rollable on a part of an outer peripheral surface of the follower rotation member, wherein the eccentric cam and the motor output shaft are press-fitted onto an outer peripheral portion of the needle bearing, the needle bearing extending over both the eccentric cam and the motor output shaft in an axial direction thereof.
 2. The valve timing control apparatus as claimed in claim 1, wherein the eccentric cam supports a rolling bearing having an outer peripheral portion that is rotatable relative to an inner peripheral portion of the rolling bearing.
 3. The valve timing control apparatus as claimed in claim 2, wherein the rolling bearing is a ball bearing.
 4. The valve timing control apparatus as claimed in claim 3, wherein the needle bearing comprises needle rollers, a center of a ball of the ball bearing is placed within a region of an axial length of the respective needle rollers.
 5. The valve timing control apparatus as claimed in claim 3, wherein the eccentric cam has an eccentric cylindrical sleeve shape having an eccentric outer peripheral surface with respect to an inner peripheral surface thereof into which the needle bearing is press-fitted.
 6. The valve timing control apparatus as claimed in claim 5, wherein the eccentric cam is arranged in an inner race of the ball bearing with a slight press-fit.
 7. The valve timing control apparatus as claimed in claim 5, wherein the motor output shaft has one axial end portion that abuts against both the eccentric cam and an inner race of the ball bearing in an axial direction of the motor output shaft.
 8. The valve timing control apparatus as claimed in claim 5, further comprising a restraining plate disposed between one axial end portion of the motor output shaft and an inner race of the ball bearing, the restraining plate cooperating with the one axial end portion of the motor output shaft to restrain an axial movement of the inner race of the ball bearing.
 9. The valve timing control apparatus as claimed in claim 1, wherein the motor output shaft and the eccentric cam each have press-fit portions press-fitted onto the outer peripheral portion of the needle bearing in the axial direction, the press-fit portion of the motor output shaft having a length shorter than that of the press-fit portion of the eccentric cam.
 10. The valve timing control apparatus as claimed in claim 3, further comprising a second ball bearing, the second ball bearing comprising an outer race that abuts on an axial end of the needle bearing, and an inner race fixed to the follower rotation member.
 11. The valve timing control apparatus as claimed in claim 10, wherein the inner race of the second ball bearing is fixed in an axial direction of the second ball bearing in such a state that the inner race is disposed between the follower rotation member and a cam bolt serving to fix the camshaft to the follower rotation member.
 12. The valve timing control apparatus as claimed in claim 11, wherein the outer race of the second ball bearing is press-fitted into an inner peripheral surface of the motor output shaft, the outer race having an outer diameter smaller than an outer diameter of the needle bearing.
 13. The valve timing control apparatus as claimed in claim 1, wherein the follower rotation member has a plurality of through-holes in a portion thereof to which one axial end portion of the eccentric cam is opposed, the through-holes being arranged in a circumferential direction of the follower rotation member.
 14. The valve timing control apparatus as claimed in claim 1, wherein the needle bearing is immersed in lubricating oil that is supplied from a side of the camshaft at least after the internal combustion engine is started.
 15. The valve timing control apparatus as claimed in claim 1, wherein the electric motor comprises a stator fixed to the drive rotation member, and a rotor rotatably disposed relative to the stator, and the electric motor is supplied with electric current from a non-rotation portion through brushes and slip rings.
 16. The valve timing control apparatus as claimed in claim 15, wherein the rotor of the electric motor has a coil winding, the stator has permanent magnet pieces, and the motor output shaft has a commutator that serves to carry out changeover of energization of the coil winding to form a magnetic flux.
 17. A valve timing control apparatus for an internal combustion engine, the internal combustion engine including a crankshaft and a camshaft, the valve timing control apparatus comprising: a drive rotation member to which a rotational force is transmitted from the crankshaft; a follower rotation member fixed to the camshaft; an electric motor comprising a rotor that is rotatable relative to the drive rotation member; a speed reducer comprising a trochoid curve-shaped internal gear portion that is rotatable with the drive rotation member, a ball bearing disposed on an inner peripheral side of the internal gear portion, the ball bearing comprising an outer race, an inner race having an outer peripheral surface eccentric relative to an inner peripheral surface thereof, a plurality of rollers disposed between the internal gear portion and the outer race of the ball bearing, and a comb-shaped cage that is rotatable with the follower rotation member, the cage supporting the plurality of rollers, the cage being rotated relative to the internal gear portion by rotation of the inner race of the ball bearing, a tubular motor output shaft fixed to an inner periphery of the rotor, the motor output shaft having an axial end that serves to restrain an axial movement of the inner race of the ball bearing, and a needle bearing that is rollable on a part of an outer peripheral surface of the follower rotation member, wherein the inner race of the ball bearing and the motor output shaft are press-fitted onto an outer peripheral portion of the needle bearing, the needle bearing extending over both the inner race of the ball bearing and the motor output shaft in an axial direction thereof.
 18. The valve timing control apparatus as claimed in claim 17, further comprising a washer disposed between one axial end portion of the motor output shaft and one axial end portion of an inner race of the ball bearing, the washer having an outer diameter larger than an inner diameter of the inner race of the ball bearing, the washer serving to restrain an axial movement of the inner race of the ball bearing.
 19. A valve timing control apparatus for an internal combustion engine, the internal combustion engine including a crankshaft and a camshaft, the valve timing control apparatus comprising: a drive rotation member to which a rotational force is transmitted from the crankshaft; a follower rotation member fixed to the camshaft; an electric motor comprising a rotor that is rotatable relative to the drive rotation member; a speed reducer comprising at least one engagement portion, the one engagement portion being disposed in a transmission path through which a rotational force is transmitted from the electric motor, the speed reducer serving to reduce a rotational force transmitted from the rotor to an input portion and transmit the rotational force reduced to the follower rotation member, a tubular motor output shaft fixed to the rotor; a sleeve disposed such that an axial end portion thereof is opposed to an axial end portion of the motor output shaft, the sleeve being fixed to the input portion of the speed reducer, and a bearing that is rollable on a part of an outer peripheral surface of the follower rotation member, wherein the sleeve and the motor output shaft are press-fitted onto an outer peripheral portion of the bearing, the bearing extending over both the sleeve and the motor output shaft in an axial direction thereof.
 20. The valve timing control apparatus as claimed in claim 19, wherein at least one of the one engagement portion of the speed reducer and the follower rotation member is changed in size so as to adjust a clearance between the one engagement portion of the speed reducer and the follower rotation member. 